1. Field of the Invention
The present invention relates to a process for continuously preparing a fiber reinforced cement (hereinafter referred to as FRC) and an apparatus for preparing the same.
2. Description of the Prior Art
Sheet forming methods such as the Hatchek method, and the Magniani method have been mainly employed for preparing asbestos cement slates and pulp cement boards useful in the preparation of FRC.
The direct spraying method and the spray-suction method have been employed for preparing glass fiber reinforced cement hereinafter referred to as GRC) sheets.
Because in the preparation of fiber reinforced cement a dewatering step is used by the application of suction, a dense sheet having high strength can be obtained and the sheets can be used in various fields.
Continuous spray-suction methods and sheet forming methods have been proposed as processes for continuously preparing GRC sheet in U.S. Pat. No. 3,974,024 and other patents. However, the processes have not been employed on an industrial scale except certain sheet forming methods. The belt filtering apparatus using suction boxes has been disclosed in Japanese Patent Publication No. 31619/1976.
In accordance with the conventional sheet forming method of preparing the GRC sheet, the glass fibers may have a directional orientation in the GRC sheet so that the sheet has different directional strength characteristics and the strength of this type of GRC sheet is relatively less than the strength of GRC sheets prepared by the direct spraying method or the spray-suction method. A process is required for continuously preparing GRC sheets having as high a strength as GRC sheets prepared by the direct spraying method and the spray-suction method. In order to achieve such a continuous process, it has been proposed to move a filter cloth on a suction box. However, when a reduced pressure is maintained in the suction box, the filter cloth of flexible material is sucked on the suction box such that it is not easily removed. Moreover, the cloth readily twists or becomes creased if forcibly removed from the suction box which can damage or tear the GRC sheet on the cloth. Accordingly, the continuous process has not been employed in industrial process.